Insulin and insulin-like growth factor (IGF) receptors have been detected in normal human brain. However, the role of IGFs in the brain is not understood. Although considered to be primarily a fetal growth factor, IGF-II levels continue to be detected at high levels in the CNS of adults, although the functional significance of this observation is unknown. Similarly, what role IGFs may play in brain tumors is unknown. We conduct studies on normal and malignant brain tissue and in cell cultures derived from these tissues to begin to understand the physiologic significance of this family of growth factors in human brain. Our studies demonstrate a high level of IGF-I receptors on low grade astrocytomas, suggesting a role for IGF-I in brain tumor oncogenesis. At least some glioma derived cell lines also produce IGFs as measured by competition in a radioreceptor assay.